1. Infections Increased susceptibility to various infections is the main, most common and most serious manifestation and consequence of immunodeficiency, and infections are also the main cause of death in patients. The younger the patient, the more frequent the infection and the more severe the disease. Infections may present as recurrent or persistent, acute or chronic. There is no significant gap between infections. The site of infection is most commonly the respiratory tract. The nature of the infection depends mainly on the type of immunodeficiency. For example, infections in the presence of humoral immunity, phagocytosis and complement deficiency are mainly caused by septic cells such as Staphylococcus, Streptococcus and S. pneumoniae, with clinical manifestations such as tracheitis, pneumonia, otitis media, septic meningitis and pyoderma. Infections in cellular immunodeficiency are mainly caused by viruses, fungi, intracellular parasitic bacteria and protozoa. The normal flora of the immunodeficient person and microorganisms with no or very weak pathogenicity in air, soil and water, such as Escherichia coli, Pseudomonas aeruginosa and Aspergillus, are very susceptible to this type of infection, which is called opportunistic infection. 2, malignant tumors World Health Organization (WHO) reported that the incidence of malignant tumors in primary immunodeficiency disease with T-cell immunodeficiency is 100-300 times higher than the normal population of the same age, with leukemia and lymphatic system tumors being the most common. The incidence of autoimmune diseases in the normal population is 0.001%-0.01%, while the incidence of autoimmune diseases in immunodeficient people can be as high as 14%, with systemic lupus erythematosus, rheumatoid arthritis and pernicious anemia being more common. 4. Multi-system involvement and variability of symptoms In terms of clinical and pathological manifestations, immunodeficiency is highly heterogeneous. Different immunodeficiencies are caused by defects in different components of the immune system, so the symptoms are different, and the performance of the same disease can be different in different patients. Immunodeficiency can involve the respiratory system, digestive system, hematopoietic system, endocrine system, bone and joint system, nervous system and skin mucosa, etc., and symptoms of corresponding dysfunction appear. 5, genetic predisposition Most primary immunodeficiency diseases have a genetic predisposition, about 1/3 for autosomal inheritance, 1/5 for sex chromosome recessive inheritance.